Solar energy collectors are generally provided with a transparent cover, usually glass to keep soil out. These collectors that are always exposed to the sky must use heavy glazing in order to withstand damage by hail or high winds. Even during quiet weather the glass may acquire dew at night, causing any soil in the atmosphere to adhere. This invention features an elongated parabolic reflector revolving around a conduit located along the focal line of the reflector. Sensing means are mounted on the reflector designed to control the rotation in order that solar energy may always be reflected onto conduit to heat the fluid. This is common practise amoung those in the art who control rotation by electrical means. What is new with this invention is that means are provided to discontinue the tracking whenever heavy clouds obscure the sun and rotate the reflector to what we might call the downward position. Under clear skies this rotation will begin shortly before sunset. Some of the prior art being the reflector facing the horizon for the night at the end of the day, but none are equipped to bring the reflector down under either day or night. This invention allows for light glazing, with more solar energy making it through to the conduit. Further all this is accomplished useing only two sensors in two separate circuits, with a commutative switch directing control to one or the other of these two circuits as a function of the position of the reflector. None of prior art can equal this for simplicity. With the commutative switch there need be no reverse rotation, for the wiring does not twist to accommodate a sensor mounted on a rotating reflector.
Further this invention discloses support for a stationary conduit, surrounded by a rotating reflector which avoids any physical contact between the two. Therefore the conduit may be light and made of the best heat absorbing material. Also no loss of solar energy where the reflector might be journaled onto the conduit.
Further the commutative switch makes possible a one-way rotation, driven by a belt and chains. These drives needs and idler on the slack side making reverse rotation difficult for the idler must be changed. With reverse rotation gearing is better, however more expansive than belt and chain drive. All prior electrical controls use reverse rotation.
Since the parobolic reflector concentrates so much solar energy on a small absorber, the conduit, the rotation of the reflector itself may be used to turn on and off a toggle switch controlling an electric pump, circulating fluid through the conduit. A thermostat is not needed here, however, a thermostat may be provided to turn off collecting operations whenever the desired temperature has been attained.
Further this invention discloses apparatus designed to adjust the reflector for azimuth manually. Bi-weekly reflector reflects to a focal line, not a point. this means that even though the setting for azimuth may be off slightly from the correct setting the solar energy will still impinge on the conduit to heat the fluid. This bi-weekly adjustments will do. Some collectors in the art use no adjustments at all, which means that they are at their best some time in the winter. This invention remains efficient the year round. Others adjust for changes of the sun's azimuth by employing electric or clock control which adds more to the cost than they are worth.
Some examples of prior art are U.S. Pat. Nos. 3,917,942; 3,996,460; 4,108,454; 4,146,785; 4,100,915; 4,107,521; 4.011,858; 4,205,659; 4,147,154; 4,086,485.
All these use electric controls that are more elaborate, use reverse rotation, and do not turn the reflector earthward for protection. None support reflector and conduit by the same frame independently of each other.
It is therefore an object of this invention to provide solar energy collecting apparatus using electrical motor means for rotating a reflector to track the sun, controlled by light sensor means,to hold the reflector at all times in the downward position, except when tracking the sun.
Further, it is an object of the present invention to provide a method of collecting solar energy, by incorporating a commutative switching apparatus to selectively direct electrical energy to a sensor mounted in a stationary housing, which forms part of a holding circuit when the reflector is at the downward position, starting rotation with adequate sunlight to a predetermined point for changeover to a tracking circuit. At this point the commutative switching apparatus will direct electrical energy from the holding circuit to a tracking circuit whose sensor is mounted on and rotating with the reflector, disposed in a housing built to restrict light to sunlight coming directly to the solar energy reflecting surface, in order that solar energy may be reflected onto a conduit stationed along the focal line of the reflector, to heat fluid passing through the conduit. The tracking circuit is set to rotate the reflector whenever less than the chosen quantity of light is received, and halting rotation whenever that chosen quantity is received, for at that position the reflecting surface of the reflector is directly facing the sun and reflecting solar energy onto the conduit. As the sun travels along its path less light will reach the tracking sensor, closing the circuit, starting the motor and thus nudging the reflector forward until with increased light rotation is halted. As the sun travels furhter along its path this operation will be repeated again and again, until the low sun fails to provide sufficient light to open the tracking circuit. From here on rotation will continue, until the commutative switching apparatus will again direct electrical energy to the holding circuit when the collector faces the downward position. Since the quantity of light reaching the holding circuit is insufficient to close that circuit, the reflector will remain halted for the night. If clouds had appeared during the tracking operation just described above at any time during the day, rotation to the downward position would have begun right then, thus completing a full revolution around the conduit.
Further it is an object of the present invention to provide solar energy collecting apparatus which incorporates back-up means to the electrical motor means to rotate the reflector to the protected position in the event power is lost during the tracking operation.
Further it is an object of this invention to provide a frame to support, independantly of each other, a stationary conduit for passing fluid to be heated by solar energy, and an elongated parabolic reflector, with an axis extending co-axially with that of the conduit.
Further, it is an object of this invention to provide means for adjusting the frame supporting the conduit and the reflector with hinges at the upper end, and extending apparatus at the lower end to be operated manually, these means to provide adjustment for the reflector and the conduit according to the azimuth of the sun.
In accordance with the invention, a solar energy collecting apparatus comprises a frame and a stationary conduit supported by the frame. A reflector is also supported by the frame for rotation around the conduit and has an energy reflecting surface to reflect solar energy onto the conduit to heat fluid being passed there through. An electric motor is operably connected to the reflector for rotating the reflector around the conduit. A control apparatus comprising a commutative switch, to direct electrical energy to one or the other of two control circuits according to the position of the reflector is provided. At the downward position, the holding circuit is in control. The holding circuit will direct electrical energy to the motor rotating the reflector with the advent of adequate sunlight to rotate the reflector to a predetermined point for changeover to a tracking circuit. The tracking circuit will direct electrical energy to the motor rotating the reflector in the absence of adequate sunlight.
The commutative switch mentioned above has four brushes set to slideably engage four rings to provide electrical transmission, with one of the rings divided into two segments, labeled night and day segments. The night segment is connected into the sensor holding circuit and the day segment into the sensor tracking circuit. The brushes are stationary and the rings rotate with the reflector, thus providing for switching as a function of the position of the reflector.